Sand casting technology of large bearing pedestal

In power station, petrochemical industry, metallurgy, ship industry and equipment manufacturing industry, there are large-scale bearing pedestal applications, such as turbine rotor support pedestal in nuclear power equipment, blade support pedestal of hydropower unit and wind turbine unit, support pedestal of large rolling mill, etc., whether these high-quality large-scale bearing pedestal can be manufactured, It has a direct impact on the quality, safety and progress of national key projects, and also shows an important significance in the national economy and people’s livelihood.

The material of bearing seat is ZG310-570, and the production property is batch production.

The casting is a large thick wall part, which is produced by sand casting according to the production program. The upper and lower moulds are made of fake boxes, mechanical sand is filled by hand, the moulds are made of phenolic modified furan resin self hardening sand, the coating is alcohol based coating, and the parting agent is made of silver graphite powder by hand for demoulding.

1. Determination of parting surface

According to the structural characteristics of the bearing pedestal, the three box curved surface is adopted. The parting scheme is of upper, middle and lower three box shape, as shown in Figure 2. The lower parting surface is a curved surface, which is modeled by a false box, that is, first make a template on the upper mold, and then fill sand to make the lower mold, so as to ensure the dimensional accuracy of the lower mold due to the support and positioning of the false box at the bottom of the upper mold, at the same time, improve the production efficiency, and then turn the box to make the upper mold; the upper parting surface is a plane.

2. Design of pouring and caving system

In the sand casting process design, the gating system is selected as the open step gating system, which is poured by the bottom pouring bag. According to the sand casting material, the gate cup is made of refractory bricks, and the gating system is connected by ceramic pipes.

The size of each component in the gating system of the sand casting is calculated by the design method of flow stopping section, and the diameter of each component of the refractory ceramic pipe in the gating system is determined according to the calculated data.

The riser is used for feeding and solidification in accordance with the sequence of iron chill strengthening. The riser is a general open riser. According to the solidification shrinkage of the steel casting, the sizes of 1 × 2 × 3 × 4 × riser are preliminarily determined as follows: 1 × riser, 3 × 3 × riser is 323 mm in diameter and 485 mm in height. 2 × riser and 4 × riser have a diameter of 336 mm and a height of 485 mm.

Shrinkage rib, also known as cutting rib, is designed to prevent hot cracking of sand castings and is mainly used in the production of steel castings. Specific reference [4] design, thickness t = (1 / 3 ~ 1 / 4) δ = 65 mm (δ is the thickness of sand casting auxiliary wall), length of bevel L = (8 ~ 12) t = 520 mm, interval d = (15 ~ 20) t = 975 mm, from the minimum interval of 975 mm, it can be concluded that only one cutting rib can be set, symmetrically arranged.

3. Sand core design

From the three-dimensional diagram of the sand casting, it can be seen that the inner cavity in the middle of the sand casting needs to be cast, and a cylindrical sand core can be designed, and the core head is square; there are four inner cavities on the two-week fixed base that need to be cast, and the shape is made according to the inner cavity of the sand casting, and air holes are left in the middle of the sand core.

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